This invention relates to a system for preventing the escape of hydrocarbon vapors to the atmosphere during the refueling of a vehicle from a service station's fuel dispensing apparatus.
Previous vapor recovery systems have included passages in the fuel dispensing nozzle for collecting vapors from the vehicle fuel tank, as well as a vapor return line for delivery of the collected vapors to the underground fuel reservoir. Each of these prior systems, however, has suffered from one or more of various drawbacks.
Some systems have relied solely upon vapor pressure within the fuel tank to push vapor through the vapor return line. To minimize resistance to vapor flow, these systems have required a large and cumbersome vapor return line. Additionally, when that return line became blocked by liquid (e.g., from fuel splashback or condensation), the vapor pressure developed in the vehicle fuel tank was usually insufficient to overcome the blockage. The result was vapor leakage to the atmosphere at the nozzle-fuel tank interface.
Other systems have employed a vacuum-assist for drawing vapor through a vapor return line. To avoid the expense of a separate vacuum pump at each service station pump housing, such systems have typically resorted to a powerful, continuously-operating blow-type vacuum pump and a complicated arrangement of electrically actuated valves for connecting the various vapor return lines to the vacuum pump when the various pumps were actuated for fuel dispensing. Acceptance of these systems has been minimal because of the expense and difficulty of both installation and maintenance. Additionally, such systems typically draw such a large volume of ambient air, relative to the volume of fuel vapor, that there is danger of an explosive mixture being formed.
Finally, it has been suggested that each fuel dispensing unit include a vacuum pump driven by the unit's conventional fuel meter and connected to a vapor return line. The well known fragility of the meter, however, renders suspect the practicality of this suggestion.